1. Technical Field
The present disclosure relates to a ceiling-embedded air conditioner. More specifically, the present disclosure relates to a ceiling-embedded air conditioner that suppresses swirling airflows generated on the back surface of a bell-mouth by rotation of a turbo fan.
2. Description of the Related Art
The ceiling-embedded air conditioner has a casing body including a heat exchanger and a blower (turbo fan). The casing body is embedded in a space formed between a ceiling slab and a ceiling panel. A flat square decorative panel is attached to the lower surface of the casing body. The decorative panel has an air inlet and an air outlet.
In the configuration described in JP-A-2012-2165, the casing body is a cuboid in shape. The turbo fan is disposed at the center of the casing body. The heat exchanger is disposed to surround the outer periphery of the turbo fan. A bell-mouth is provided between the air inlet and the turbo fan. The bell-mouth guides the air, which is taken into the casing body from the air inlet, to the inside of the turbo fan.
The turbo fan has a main plate, a shroud, and a plurality of blades. The main plate has a hub, to which a rotation shaft is fixed, at the center. The shroud is disposed to be opposite to the direction of axis of the rotation shaft relative to the main plate. The plurality of blades is disposed between the main plate and the shroud. The shroud has an opening at the center through which the bell-mouth is partially inserted into the turbo fan.
The bell-mouth has a base portion and a suction guide portion. The base portion is formed in a square shape corresponding to the shape of the air inlet. The suction guide portion is formed in a trumpet shape from the center of the base portion toward the inside of the turbo fan. As the turbo fan is driven, the air is sucked from the air inlet through the bell-mouth to the inside of the turbo fan (refer to JP-A-2012-2165, FIG. 2).
The air blown from the turbo fan is directed to the surrounding heat exchanger, and is heat-exchanged with a refrigerant through the spaces between heat-radiation fins in the heat exchanger. After that, the air is blown from the air outlet into the room through a blowing path. The blowing range of the turbo fan in the axial direction depends on the axial height of the outlet. In general, the axial height of the outlet is set to be lower than the height of the heat exchanger. This causes unevenness in wind speed distribution at the portion of the heat exchanger opposed to the outlet and the portion of the heat exchanger separated from the outlet. The unevenness results in unbalanced heat exchange.
As another problem, there is high blowing resistance at the back surface side of the blowing path opposite to the suction guide portion side of the bell-mouth. Accordingly, part of the air leaks from the gap formed between the bell-mouth and the turbo fan into the inside of the turbo fan (recirculation). Therefore, the air not passing through the heat exchanger is retained on the back surface side of the bell-mouth. As the turbo fan rotates, the retained air swirls along the back surface of the bell-mouth opposite to the air suction surface on the air inlet side. That is, swirling airflows are generated. The generation of the swirling airflows leads to reduction in the amount of wind flowing into the heat exchanger. This results in an unsmooth flow of air with lower heat-exchange efficiency.
According to the technique described in JP-A-2007-100548, radial ribs are provided on the back surface of the shroud to suppress loss of air blow. Accordingly, the air approaching the gap formed between the bell-mouth and the shroud is forcibly pushed back to the outside in radial direction.
However, the method described in JP-A-2007-100548 does not solve the swirling airflow problem and thus is less effective in preventing reduction in heat-exchange efficiency. In addition, providing the ribs may increase wind noise and vibration.